23-31: Supraventricular Tachycardia (SVT)

ECG Findings

• Narrow complex, regular tachycardia, rate usually > 140 bpm.

• Absent, retrograde, or unusual P waves.

• P waves may be buried in the QRS complex.

Pearls

1. SVT occurs when the SA node rhythm is superseded by a faster rhythm, usually originating in the AV node.

2. Three common types are:

   1. Atrial tachycardia—originates from an ectopic focus in the atrium. P waves may have an unusual morphology or may be hidden by the preceding T wave.

   2. AV nodal reentrant tachycardia (AVNRT) occurs when an electrical impulse reenters the AV node in a circular pattern causing rapid depolarizations of the ventricles. Since the AV node is the origin of the atrial depolarization, the P-wave deflection should be inverted if seen (eg, downgoing in II, III, aVF).

   3. AV reentrant tachycardia (AVRT) as seen with bypass tracts outside of the AV node (WPW). Instead of intranodal reentrant activity as seen with AVNRT, an accessory tract provides the reentrant pathway to propagate the tachycardia.